Cluster

HBBFT consensus on each node, and whether the nodes are in step.

Read from each node's consensus log. A node is in sync when it reached consensus in the last 15 s within 5 rounds of the leader; lagging or catching up when it's further behind; stalled when it hasn't reached consensus for 15 s; recovering when that follows a restart or recovery. With 4 nodes, consensus needs 3, so one node can be down.